1. Field of the Invention
The present invention relates to a temperature controller having a bimetallic switching mechanism that switches in response to a predetermined temperature, a lower housing part receiving the switching mechanism, a cover part closing off the lower housing part, and a substantially inert polyimide film that is arranged between the lower housing part and the cover part.
2. Discussion
Temperature controllers of this kind are known from the related art. In the case of the known temperature controllers, the lower housing part and the cover part are made of conductive material, preferably of metal, so that they are very stable and pressure-resistant.
As a rule, the bimetallic switching mechanism comprises a spring disk that is braced at its rim against the bottom of the lower housing part and carries in its center a movable contact element which it presses against the inside of the cover part, where a fixed countercontact is arranged. A bimetallic snap disk, which below its switching temperature rests unconstrainedly on the spring disk, is slipped over the moving contact element. Contact to a temperature controller of this kind is made via the cover part and the lower housing part, the current flowing from the cover part through the countercontact and the spring disk to the lower housing part.
If the temperature of the bimetallic snap disk increases impermissibly, it snaps over from its convex shape into a concave shape, in which it lifts the movable contact element away from the countercontact against the force of the spring disk and thus opens the circuit. It is necessary for this purpose that the cover part be insulated with respect to the lower housing part, which is accomplished by means of a substantially inert polyimide film.
The substantially inert polyimide film of the present invention also covers the inner side of the cover part, so that the bimetallic snap disk which, in its high temperature position, is braced at its rim cannot produce a short-circuit between the cover part and the spring disk.
It is known to use, instead of the substantially inert polyimide film, a different insulating film that can be made, for example, of a polyamide or aramide paper or of polytetrafluoroethylene. The thickness of the substantially inert polyimide film in one embodiment is 75 micrometers, this thickness being determined by the desired electric strength. It should be mentioned that in the open-circuit state, there is a voltage drop across the substantially inert polyimide film which can correspond to the level of the mains voltage.
It is advantageous for the operation of the temperature controller as described so far that no dust, moisture, or liquid get into the interior of the temperature controller, so as to prevent any impairment of the function of the bimetallic switching mechanism. Dust and liquid can, for example, result in undesirable tracking currents or insulated areas which can negatively influence the reliable operation of the temperature controller. Damage to the switching mechanism can also occur.
In order to achieve the required sealing, in the related art the temperature controller, equipped with connecting leads, is encased with epoxy, silicone, or other encasing compounds, either entirely or only on the surfaces at which there are opportunities for dust, water, oil, etc. to penetrate. These encasing operations require additional cost-intensive operations.
It is furthermore known to slide heat-shrink tubing over the temperature controllers, once they have been equipped with connecting leads, in order to achieve electrical insulation.